lol, the △ is net slang! Most regular Japanese people have never heard of it. I've only ever seen it at ニコニコ動画
– JeshizaemonJun 7 '11 at 20:27

1

Number of google hits is not a reliable metric for judging the general popularity of a word or phrase. It is possible to make a google search claim thousands or even millions of hits, but then you scroll down and see there are only three pages of results (30 or so hits).
– Kef SchecterOct 27 '11 at 18:36

But I got 346,000 for かっこ好い, but even that it's still strange to dismiss an entry from EDICT ..
– LukmanJun 7 '11 at 16:22

@Lukman, I think you need to put quotes like "かっこ好い", when you search.
– YOUJun 7 '11 at 16:28

1

@Lukman: Did you encapsulate it in double quotes? Google will search for alternate kanji unless you tell it to search for the exact characters you enter by putting it in like this: "かっこ好い"
– Derek SchaabJun 7 '11 at 16:30

1

But t3h Google cannot lie! ;) It may not be hard proof, but it's still better than pure speculation or anecdotal evidence from a handful of native speakers. Imagine asking a question like this 20 years ago...
– Derek SchaabJun 7 '11 at 16:33

2

See my comment about the unreliability of Google hits in the comments of the answer posted by 'YOU'.
– Kef SchecterOct 27 '11 at 18:38

In general, people will use the hiragana version かっこいい. If you talk with friends and use 格好いい, they'll most likely be thrown off for a bit.

かわいい has a similar usage, with the reason being that just using hiragana makes it feel "cuter" since children without kanji experience are more likely to use it.

It's important to note that you might also find the net-slang version littered about message boards and other popular sites かっけえええええ. Because it's slang, you shouldn't use it around people you don't know though!

かっこ好い

かっこいい and カッコいい seem to be more common in dialog, while 格好いい is more common in prose. If you were quoting someone or writing an informal email, tweet, etc., you would probably use かっこいい or カッコいい. But if you were writing from a third-person perspective, you would probably use 格好いい.

So you have 2 ways to write it:
かっこいい & かっこういい
The only variants I encountered in mangas until now were:
カッコイイ and 格好いい (the latter is long, as you can also see, when you write かっこう and presse enter, you'll get the kanji's, but not if you write only かっこ)